1. Field of the Invention
The present invention relates to a windscreen washer pump, and particularly to a washer pump for use with a vehicle, which serves to supply washer fluid to two systems for the windscreen.
2. Description of the Related Art
There has widely been used to date vehicles of the two wiper type each of which is provided with two wipers both on the front and rear sides. In a two-wiper type vehicle, it is preferable to differentiate between the delivery pressure of washer fluid to the front glass and that of the washer fluid to the rear glass, both glasses being subjected to the various influences such as wind pressure or the like. It is especially preferable to supply washer fluid at high delivery pressure to the front glass which is susceptible to wind pressure or the like and to supply washer fluid at low delivery pressure to the rear glass which is less susceptible to the wind pressure.
Thus, two washer pumps having different delivery pressure are mounted on a conventional vehicle and the washer fluid is supplied to the front and rear glasses with different delivery pressure by using the respective washer pumps.
However, the use of two different pumps for the supply of washer fluid to the two systems not only incurs an increase in manufacturing cost but trouble often develops on the positions where the two pumps are located.
Accordingly, it has heretofore been proposed to selectively supply washer fluid to the front and rear sides by using a single washer pump (Japanese Patent Laid-Open No. 60-6096).
However, the prior art is accompanied by the problem that the delivery pressure of washer fluid to the front side is not differentiated from that of the washer fluid to the rear side, although there is no problem from the standpoint of manufacturing cost and the position where two washer pumps are employed.
Thus, when the delivery pressure of the washer pump is set to a higher value in relation to the front glass, the delivery pressure of the washer fluid to the rear glass is so high that a reduction in efficiency takes place due to the spray of the fluid or the like. On the other hand, when the delivery pressure of the washer pump is set to a lower value in relation to the rear glass, a substantial quantity of washer fluid cannot be supplied to the front glass. In particular, when the wind pressure is high as in the case where the vehicle is running at high speed, the landing point of the washer fluid onto the front glass varies correspondingly and hence the wiping ability of the front glass is deteriorated.